Method of audio encoding

ABSTRACT

There is described a method of encoding an input signal ( 20 ) to generate a corresponding encoded output signal ( 30 ), and also encoders ( 10 ) arranged to implement the method. The method comprises steps of: (a) distributing the input signal to sub-encoders ( 300, 310, 320 ) of the encoder ( 10 ); (b) processing the distributed input signal ( 20 ) at the sub-encoders ( 300, 310, 320 ) to generate corresponding representative parameter outputs ( 200, 210, 220 ) from the sub-encoders ( 300, 310, 320 ); and (c) combining the parameter outputs ( 200, 210, 220 ) of the sub-encoders ( 300, 310, 320 ) to generate the encoded output signal ( 30 ). Processing of the input signal ( 20 ) in the sub-encoders ( 300, 310, 320 ) involves segmenting the input signal ( 20 ) for analysis, such segments having associated temporal durations which are dynamically variable at least partially in response to information content present in the input signal ( 20 ). Such varying segment duration is capable of improving perceptual encoding quality and enhancing data compression achievable.

FIELD OF THE INVENTION

The present invention relates to methods of encoding audio signals.Moreover, the invention also concerns encoders operating according tothe method, and also an arrangement of encoded data generated by suchencoders. Furthermore, the invention additionally relates to decodersoperable to decode data generated by such encoders. Additionally, theinvention also concerns an encoding-decoding system utilizing themethods of encoding.

BACKGROUND TO THE INVENTION

Audio encoders are well known. These encoders are operable to receiveone or more input audio signals and process them to generatecorresponding bit-streams of encoded output data. Such processingexecuted within the audio encoders involves partitioning the one or moreinput signals into segments, and then processing each segment togenerate its corresponding portion of data for inclusion in the encodingoutput data.

Conventional methods of creating such bit-streams employ fixed uniformtime segments. Beneficially, the segments are at least partiallyoverlapping. An example of an encoder performing in this manner isPhilips Electronics N.V.'s proprietary SSC codec whose mode of operationis now included in a known international standard MPEG 4 extension 2,namely text of ISO/IEC 14496-3:2002/PDAM 2 concerning “Parametric codingfor High Quality Audio”.

Other methods of encoding audio signals have been proposed. For example,in a published international PCT application no. PCT/SE00/01887 (WO01/26095), there are described modern audio encoders which employadaptive window switching, namely the audio encoders switch time segmentlengths depending on input signal statistics. In one implementation,non-uniform time and frequency sampling of a spectral envelope of aninput signal is achieved by adaptively grouping sub-band samples from afixed size filter-bank into frequency bands and time segments, each ofwhich generates one envelope sample. This allows for instantaneousselection of arbitrary time and frequency resolution within the limitsof the filter-bank. Such encoders preferably default to relatively longtime segments and a fine frequency resolution. In the temporal vicinityof signal transients, relatively shorter time segments are used, wherebylarger frequency steps can be employed in order to keep data size withinlimits. Moreover, to enhance benefits from such non-uniform temporalsampling, variable length of bit-stream frames are used.

SUMMARY OF THE INVENTION

The inventors have appreciated that, when encoding audio signals, it ismore beneficial in terms of bit-rate and/or perceptual distortion to usevariable segmentation, for example as described in the foregoing. Forexample, it is technically advantageous to use longer segments forsteady tones, shorter segments for rapidly changing tones, to startsegments immediately preceding transients, and so forth. In particular,the inventors have envisaged that it is further beneficial to employdifferent time segmentation patterns for different sub-coding methodswith the same encoder.

An object of the present invention is to provide an enhanced method ofsignal encoding utilizing dynamically variable signal segmenting.

According to a first aspect of the present invention, there is provideda method of encoding one or more input signals to generate one or morecorresponding encoded output signals, the method comprising steps of:

(a) receiving the one or more input signals and distributing themsuitably to sub-encoders of an encoder;

(b) processing the one or more input signals distributed to thesub-encoders in respect of one or more signal characteristics of the oneor more distributed input signals to generate correspondingrepresentative parameter outputs from the sub-encoders;

(c) combining the parameter outputs of the sub-encoders to generate theone or more encoded output signals,

wherein processing of the one or more distributed input signals in thesub-encoders involves segmenting the one or more distributed inputsignals into segments for analysis, said segments having associatedtemporal durations which are dynamically variable at least partially inresponse to information content present in the one or more distributedinput signals.

The invention is of advantage in that the method of encoding is capableof providing one or more of: perceptually better encoding quality,enhanced data compression.

Preferably, in the method, the segments of the one or more distributedinput signals are processed mutually asynchronously in the sub-encoders.Such asynchronous operation is capable of enabling each sub-encoder tofunction optimally with regard to its respective aspect of signalprocessing executed in the method.

Preferably, in the method, the segments of the one or more distributedinput signals with respect to each sub-encoder are at least partiallytemporally overlapping. Such overlapping is of benefit in that itreduces abrupt changes in signal characteristic from one segment toanother temporally neighboring thereto.

Preferably, in the method, the sub-encoders are arranged to process theone or more distributed input signals in respect of at least one of:sinusoidal input signal information content, input signal waveforminformation content, input signal noise information content.

Preferably, in the method, the segmenting of the one or more distributedinput signals involves at least one of:

(a) generating relatively longer segments for steady tones present inthe one or more distributed input signals;

(b) generating relatively shorter segments for rapidly changing tonespresent in the one or more distributed input signals; and

(c) arranging for segments to end substantially immediately precedingtransients occurring in the one or more distributed input signals.

Such adaptation of the segments depending in input signal content isbeneficial for improving the perceptual quality of encoding provided bythe method.

Preferably, in the method, the encoded output signal is sub-divided intoframes wherein each frame includes information relating to segmentsprovided from the sub-encoders which commence within a temporal durationassociated with the frame. This definition for the frames renders iteasier to provide random access within a sequence of encoded datagenerated using the method. Thus, more preferably, in the method, thesegments included within each frame are arranged in chronological order.Yet more preferably, in the method, each frame additionally includesparameter data describing a temporal duration between a temporal startof the frame and a first segment commencing after the frame's start.

Preferably, in the method, a number of segments included within eachframe is dynamically variable depending upon information content presentin the one or more distributed input signals.

According to a second aspect of the present invention, there is providedan encoder operable to process one or more input signals and generatecorresponding one or more encoded output signals, the encoder beingarranged to implement a method according to the first aspect of theinvention.

According to a third aspect of the present invention, there is provideda decoder operable to receive one or more encoded output signals anddecode them to generate one or more corresponding decoded signals, thedecoder being arranged to be capable of processing the one or moreencoded output signals as generated by a method according to the firstaspect of the invention.

According to a fourth aspect of the present invention, there is provideda signal processing system arranged to include an encoder according tothe second aspect of the invention and a decoder according to the thirdaspect of the invention.

According to a sixth aspect of the present invention, there is providedencoded output signal data generated by employing a method according tothe first aspect of the invention, said data being conveyed by way of adata carrier. More preferably, the data carrier comprises at least oneof a communication network and a data storage medium.

According to a seventh aspect of the present invention, there isprovided software executable on computer hardware for implementing amethod according to the first aspect of the invention.

It will be appreciated that features of the invention are susceptible tobeing combined in any combination without departing from the scope ofthe invention.

DESCRIPTION OF THE DIAGRAMS

Embodiments of the invention will now be described, by way of exampleonly, with reference to the following diagrams wherein:

FIG. 1 is a schematic illustration of an encoder operable to receive anaudio input signal and process it to generate a corresponding encodedoutput signal in the form of an encoded output bit-stream;

FIG. 2 is a temporal diagram illustrating processing occurring withinthe encoder of FIG. 1 utilizing fixed segmentation as known in the art;

FIG. 3 is a temporal diagram illustrating processing occurring withinthe encoder of FIG. 1 utilizing variable segmentation according to thepresent invention;

FIG. 4 is a schematic illustration of an encoder according to theinvention, the encoder having its associated sub-encoders configured ina parallel manner;

FIG. 5 is a schematic illustration of an encoder according to theinvention, the encoder having its associated sub-encoders configured ina cascaded manner; and

FIG. 6 is a schematic diagram of a decoder according to inventionoperable to decode encoded data generated by encoders according to theinvention.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

In FIG. 1, there is shown a known encoder 10 operable to receive aninput signal 20, namely S_(i), and encode the signal 20 to generatecorresponding encoded output data 30, namely BS_(O). The output data 30is in the form of a bit-stream.

Contemporary implementations of the encoder 10 rely on being able todivide the input signal 20 into segments of equal length as depicted inFIG. 2; to simplify description, arches in FIG. 2 indicate segmentintervals where there is no mutual overlap although, in practice, someoverlap is preferably utilized. The overlap employed in the encoder 10is optionally arranged to be variable, for example made variable withresponse to information content in the input signal 20; beneficially,for transients present in the input signal 20, no or relatively littleoverlap is employed to avoid pre-echo effects arising. There is shown atemporal graph in FIG. 2 where elapsed time (T) is denoted by anabscissa axis 50. The signal 20 is divided into frames, for exampleframes F1, F2, F3, which are mutually of similar time duration. In theencoder 10, the signal 20 is analyzed and various types of parametersdescribing the signal 20 are determined; preferably, these parametersconcern:

(a) transient signal information content denoted by 100;

(b) sinusoidal signal information content denoted by 110; and

(c) noise-related signal information content denoted by 120.

Each frame F1 to F3 is further subdivided into segments in respect ofeach type of parameter as illustrated, for example the frames F1 to F3comprise segments t₁ to t₁₂ regarding transient information content,segments s₁ to s₁₂ regarding sinusoidal information content, andsegments n₁ to n₁₂ regarding noise information content. Each segmentgives rise to one or more parameters describing a part of the signal 20giving rise to the segment, these one or more parameters being includedin the output 30.

An example of the encoder 10 is a proprietary Philips SSC codec whichemploys segments of substantially 16 ms duration wherein the segmentsare at least partially overlapped. Moreover, the codec employs threedifferent sub-coding methods and is operable to output parametersassociated with the segments into the bit-stream at the output 30 on asegment-by-segment basis, time-differentially where appropriate.

In the encoder 10, parameters from several consecutive segments form acorresponding frame: for example the frame F1 comprises the segments t₁to t₄, s₁ to s₄ and n₁ to n₄. On account of the segments being of equallength, the frames F1 to F3 are also updated at a uniform rate.Moreover, each of the frames F1 to F3 is almost self-sufficient whichrenders the bit-stream output 30 suitable for streaming over acommunication network, for example the Internet, or storing onto a datacarrier providing for serial writing thereto and serial readouttherefrom, for example an audio CD. In the graph of FIG. 2, althoughonly three frames F1 to F3 are shown to illustrate fixed time-durationsegmentation, it will be appreciated that the signal 20 is representedby more than three fixed-duration frames in the output signal 30depending on duration of program content conveyed in the signal 20.

In case of packet-loss during transmission of the output 30, for exampleover a communication network such as the Internet or wireless network,error propagation for frames and segments of fixed duration will belimited, thereby potentially allowing for error concealment. Moreover,such fixed duration also allows for commencement of playback at almostany given time, and therefore corresponds substantially to randomaccess.

Despite many beneficial characteristics arising from utilizingconventional fixed duration segments and associated frames, theinventors have appreciated that advantages can be derived fromimplementing the encoder 10 to employ segments having variable duration.Moreover, further benefits in terms of data compression and bettersubjective replay quality can be derived from employing differentsegments for each parameter type. In other words, variable segmentduration in response to input signal content provides benefits regardingbit-rate and perceptual distortion.

In particular, the inventors have found that it is preferable:

(a) to employ relatively longer segments for substantially steady tones;

(b) to employ relatively shorter segments for rapidly changing tones;and

(c) to arrange segments to start immediately preceding, namelytemporally in front of, transients in the input signal 20.

Thus, it is beneficial to employ mutually different time segmentationpatterns for different sub-coding methods, namely generation ofdifferent parameter types, as will be described later with reference toFIG. 3.

In FIG. 3, there is shown a temporal graph of parameters output from theencoder 20 when implemented in a manner according to the presentinvention. The temporal graph includes the aforementioned abscissa axis50 denoting time (T) and three types of parameter output, namely:

(a) segments s₁ to s₁₂ corresponding to parameters describing sinusoidalinformation present in the input signal 20, these segments being denotedby a group 200;

(b) segments w₁ to w₁₂ corresponding to parameters describingcharacteristics of waveforms present in the input signal 10, thesesegments being denoted by a group 210; and

(c) segments n₁ to n₁₂ corresponding to parameters describing noiseinformation present in the input signal 20, these segments being denotedby a group 220.

Parameters corresponding to the groups 200, 210, 220 are combined togenerate the output 30. It will be appreciated that the groups 200, 210,220 preferably correspond to three sub-coders included within theencoder 20 as illustrated in FIG. 4, although it will be appreciatedthat other numbers of sub-coders are susceptible to being employedpursuant to the present invention.

In FIG. 4, the encoder 10 operable to output data as presented in FIG. 3is implemented as shown where sub-coders 300, 310, 320 are coupled inparallel to receive input signals 350, 360, 370 respectively derived viaa splitter 380 from the input signal 20 and generate correspondingparameter outputs corresponding to the parameter groups 200, 210, 220respectively. Optionally, the splitter 380 is arranged to providemutually similar input signals 350, 360, 370 to the sub-encoders 300,310, 320. Alternatively, one or more of these input signals 350, 360,370 can be arranged to be mutually different in order to assistprocessing executed within the encoder 10. The parameter outputs fromthe sub-coders 300, 310, 320 are connected to a multiplexer 400 whichgenerates the output 30.

Several aspects are to be identified in FIG. 3 which differentiate itfrom FIG. 2, namely:

(a) the input signal 20 is represented by sinusoidal descriptiveparameters, waveform descriptive parameters and noise descriptiveparameters in contrast to FIG. 2 wherein transient descriptiveparameters, sinusoidal parameters and noise descriptive parameters areemployed;(b) although nominal positions of the frames F1 to F3 are shown in FIG.3, not all of the segments end at boundaries of the frames F1 to F3 incontradistinction to FIG. 2 wherein synchronism is shown;(c) segments in the different groups 200, 210, 220 are of mutuallydifferent duration; and(d) segments within each group 200, 210 have mutually differentdurations, although the encoder 10 is capable of supporting more regularconstant duration segmentation, for example for the group 220, whereinformation present in the input signal 20 with regard to noise contentdictates that constant-duration segment encoding is beneficial; in otherwords, the encoder 10 operating according to the invention is preferablycapable of switching between fixed segment duration and variable segmentduration depending upon the nature of the input signal 20.

If required, the encoder 10 operating according to the invention canarrange for its parameter groups multiplexed at the output 30 toterminate simultaneously, thereby forming relatively larger frames;preferably, the output 30 from the encoder 10 operating according to theinvention is subdivided into uniform frames of 100 ms length.Preferably, the duration of the frames is determined based on a targetand a peak bit-rate constraints communicated to the encoder 10. Theseconstraints are preferably defined by a communication network to whichthe encoder 10 is coupled.

In the output data 30 generated according to the invention, parametersassociated with the segments are grouped into data packets in such a waythat each packet carries information about all segments starting in agiven frame. Such an arrangement of data is illustrated in FIG. 3.

Based on a segmentation pattern for the three frames illustrated in FIG.3, the output data 30 includes a sequence of data as presented in Table1:

TABLE 1 Frame Sequence of segment data packets included in the output 301 s₁; s₂; s₃; w₁; w₂; w₃; n₁; n₂; n₃; n₄ 2 w₄; n₅; n₆; n₇; n₈ 3 s₄; s₅,w₅; w₆; n₉; n₁₀; n₁₁; n₁₂ 4 . . .

The output 30 preferably also includes additional parameters conveyinginformation concerning a distance between of a given frame and a firstfollowing segment thereto for each sub-coder. These additionalparameters preferably represent a small proportion of the output data,for example less than 5%. Moreover, the inventors have found thatintra-segment encoding is potentially as effective as time-differentialencoding which, for example, intra-segment encoding allows for startingplayback at a first segment in any given frame without experienceencoded signal degradation, for example decoded audio qualitydegradation. An encoding scheme represented, for example, by Table 1 isalso capable of providing random access and error concealment.

It will be appreciated that encoders according to the invention, forexample as illustrated in FIG. 4, are susceptible of being implementedusing one or more computing devices operating under software control.Alternatively, or additionally, the encoders are implementable in theform of application specific integrated circuits (ASICs).

The encoder 10 illustrated in FIG. 4 is configured so that itssub-encoders 300, 310, 320 are arranged in a parallel manner. It will beappreciated that other configurations for the encoder 10 are alsopossible. For example, in FIG. 5, there is shown the encoder 10 with itssub-encoders 300, 310, 320 coupled in a cascaded manner by including twosubtraction units 450, 460. Whereas the first sub-encoder 300 in FIG. 5receives the input signal 20 distributed thereto, the second and thirdsub-encoders receive progressively residual signals as features of theinput signal 20 are encoded into the output 30. The cascadedconfiguration for the encoder 10 presented in FIG. 5 is of benefit inthat encoding errors, namely inaccuracies arising in operation of thesub-encoders, can at least partially be corrected by later sub-encoders310, 320, thereby potentially resulting in perceptually better encodingquality in comparison to the encoder 10 of FIG. 4.

To complement the encoder according to the invention, correspondingdecoders are operable to receive the output 30 and reconstitute arepresentation of the input signal S_(i); for example, such a decoder isillustrated in FIG. 6 and indicated generally by 500. The decoder 500 ispreferably implemented with a plurality of sub-decoders, for examplesub-decoders 510, 520, 530 which are capable of operating mutuallyasynchronously to process the bit-stream output 30. Moreover, thedecoder 500 is preferably implemented as one or more ASICs and/orsoftware operating on computing hardware. Although the decoder 500 isshown with its sub-encoders 510, 520, 530 coupled in a parallelconfiguration, it will be appreciated that the decoder 500 can also beimplemented in a cascaded manner akin to that of the encoder 10illustrated in FIG. 5.

It will be appreciated that embodiments of the invention described inthe foregoing are susceptible to being modified without departing fromthe scope of the invention as defined by the accompanying claims.

In the accompanying claims, numerals and other symbols included withinbrackets/parenthesize are included to assist understanding of the claimsand are not intended to limit the scope of the claims in any way.

Expressions such as “comprise”, “include”, “incorporate”, “contain”,“is” and “have” are to be construed in a non-exclusive manner wheninterpreting the description and its associated claims, namely construedto allow for other items or components which are not explicitly definedalso to be present. Reference to the singular is also to be construed inbe a reference to the plural and vice versa.

1. A method of encoding one or more input signals via an encoder togenerate one or more corresponding encoded output signals, the methodcomprising: (a) receiving, at an input of the encoder, the one or moreinput signals and distributing the one or more input signals, via asplitter, to sub-encoders of the encoder; (b) processing, at thesub-encoders, the one or more input signals distributed to thesub-encoders with respect to one or more signal characteristics of theone or more distributed input signals to generate correspondingrepresentative types of parameter outputs from the sub-encoders, whereinthe representative types of parameter outputs include sinusoidaldescriptive parameters, waveform descriptive parameters, and noisedescriptive parameters; and (c) combining the parameter outputs of thesub-encoders, via a multiplexer, to generate the one or more encodedoutput signals of the encoder, wherein processing of the one or moredistributed input signals in the sub-encoders involves segmenting theone or more distributed input signals into segments for analysis, saidsegments having associated temporal durations which are dynamicallyvariable at least partially in response to information content presentin the one or more distributed input signals, further wherein thesegmenting includes dynamically variable signal segmenting of the one ormore distributed input signals employing mutually different timesegmentation patterns for different sub-coding corresponding togeneration of different parameter types of respective sub-coders withinthe encoder and comprises: (i) generating relatively longer segments forsteady tones present in the one or more distributed input signals; (ii)generating relatively shorter segments for rapidly changing tonespresent in the one or more distributed input signals; and (iii)arranging for segments to end substantially immediately precedingtransients occurring in the one or more distributed input signals,wherein the encoded output signal of the encoder is sub-divided intoframes, each frame including information relating to all segments of thedifferent parameter types provided from the sub-encoders which commencewithin a temporal duration associated with a respective frame, furtherwherein not all of the segments end at boundaries of the frames, andfurther wherein segments of different groups of parameter types ofsinusoidal information, waveform information, and noise information areof mutually different duration, and still further wherein segmentswithin each group of a respective parameter type of sinusoidalinformation and waveform information have mutually different durations.2. The method according to claim 1, further comprising: arranging thesub-encoders in a cascaded manner via subtraction units to accommodateprogressively residual encoding residues of encoding errors arising fromearlier sub-encoders and partially corrected by later sub-encoders ofthe sub-encoders.
 3. The method of encoding according to claim 1,wherein the segments of the one or more distributed input signals areprocessed mutually asynchronously in the sub-encoders.
 4. The methodaccording to claim 1, wherein the segments of the one or moredistributed input signals with respect to each sub-encoder are at leastpartially temporally overlapping.
 5. The method according to claim 1,wherein the processing at the sub-encoders includes processing the oneor more distributed input signals with respect to: (i) sinusoidal inputsignal information content, (ii) input signal waveform informationcontent, and (iii) input signal noise information content.
 6. The methodaccording to claim 1, wherein the encoded output signal is sub-dividedinto frames wherein each frame includes parameters associated with thesegments, grouped into data packets, wherein each data packet carriesinformation relating to all segments provided from the sub-encoderswhich commence within a temporal duration associated with thecorresponding frame.
 7. The method according to claim 6, wherein thesegments included within each frame are arranged in chronological order.8. The method according to claim 7, wherein each frame additionallyincludes parameter data describing a temporal duration between atemporal start of the frame and a first segment commencing after theframe's start.
 9. The method according to claim 6, wherein a number ofsegments included within each frame is dynamically variable dependingupon information content present in the one or more distributed inputsignals.
 10. A decoder operable to receive one or more encoded outputsignals and decode the one or more encoded output signals to generateone or more corresponding decoded signals, the decoder being configuredto process the one or more encoded output signals as generated by amethod according to claim
 1. 11. A non-transitory computer-readablemedium embodied with computer program code for being loaded into amemory and executable on computer hardware for implementing a methodaccording to claim
 1. 12. An encoder operable to process one or moreinput signals and generate corresponding one or more encoded outputsignals, the encoder comprising: (a) an input for receiving the one ormore input signals and a splitter for distributing the one or more inputsignals to sub-encoders of the encoder; (b) the sub-encoders forprocessing the one or more input signals distributed to the sub-encoderswith respect to one or more signal characteristics of the one or moredistributed input signals to generate corresponding representative typesof parameter outputs from the sub-encoders, wherein the representativetypes of parameter outputs include sinusoidal descriptive parameters,waveform descriptive parameters, and noise descriptive parameters; and(c) a multiplexer for combining the parameter outputs of thesub-encoders to generate the one or more encoded output signals of theencoder, wherein processing of the one or more distributed input signalsin the sub-encoders involves segmenting the one or more distributedinput signals into segments for analysis, said segments havingassociated temporal durations which are dynamically variable at leastpartially in response to information content present in the one or moredistributed input signals, further wherein the segmenting includesdynamically variable signal segmenting of the one or more distributedinput signals employing mutually different time segmentation patternsfor different sub-coding corresponding to generation of differentparameter types of respective sub-coders within the encoder andcomprises: (i) generating relatively longer segments for steady tonespresent in the one or more distributed input signals; (ii) generatingrelatively shorter segments for rapidly changing tones present in theone or more distributed input signals; and (iii) arranging for segmentsto end substantially immediately preceding transients occurring in theone or more distributed input signals, wherein the encoded output signalof the encoder is sub-divided into frames, each frame includinginformation relating to all segments of the different parameter typesprovided from the sub-encoders which commence within a temporal durationassociated with a respective frame, further wherein not all of thesegments end at boundaries of the frames, and further wherein segmentsof different groups of parameter types of sinusoidal information,waveform information, and noise information are of mutually differentduration, and still further wherein segments within each group of arespective parameter type of sinusoidal information and waveforminformation have mutually different durations.
 13. A signal processingsystem arranged to include an encoder according to claim 11 and adecoder according to claim
 10. 14. A non-transitory data storage mediumencoded with data representing an encoded input signal, the encodedinput signal having been encoded via a method comprising: (a) receiving,at an input of the encoder, the one or more input signals anddistributing the one or more input signals, via a splitter, tosub-encoders of the encoder; (b) processing, at the sub-encoders, theone or more input signals distributed to the sub-encoders with respectto one or more signal characteristics of the one or more distributedinput signals to generate corresponding representative types ofparameter outputs from the sub-encoders, wherein the representativetypes of parameter outputs include sinusoidal descriptive parameters,waveform descriptive parameters, and noise descriptive parameters; and(c) combining the parameter outputs of the sub-encoders, via amultiplexer, to generate the one or more encoded output signals of theencoder, wherein processing of the one or more distributed input signalsin the sub-encoders involves segmenting the one or more distributedinput signals into segments for analysis, said segments havingassociated temporal durations which are dynamically variable at leastpartially in response to information content present in the one or moredistributed input signals, further wherein the segmenting includesdynamically variable signal segmenting of the one or more distributedinput signals employing mutually different time segmentation patternsfor different sub-coding corresponding to generation of differentparameter types of respective sub-coders within the encoder andcomprises: (i) generating relatively longer segments for steady tonespresent in the one or more distributed input signals; (ii) generatingrelatively shorter segments for rapidly changing tones present in theone or more distributed input signals; and (iii) arranging for segmentsto end substantially immediately preceding transients occurring in theone or more distributed input signals, wherein the encoded output signalof the encoder is sub-divided into frames, each frame includinginformation relating to all segments of the different parameter typesprovided from the sub-encoders which commence within a temporal durationassociated with a respective frame, further wherein not all of thesegments end at boundaries of the frames, and further wherein segmentsof different groups of parameter types of sinusoidal information,waveform information, and noise information are of mutually differentduration, and still further wherein segments within each group of arespective parameter type of sinusoidal information and waveforminformation have mutually different durations.